When communicating under an air-interface protocol, such as WiMAX, a subscriber station may be configured to switch to and operate in a power-saving mode during periods of lower activity and/or inactivity. When operating in a power-saving mode, the subscriber station may disable certain functions, such as its systems for reception and/or scanning, in order to save power. By operating in sleep mode, the subscriber station may conserve power without disconnecting from the access network, thus eliminating the need to reconnect with the access network when the subscriber station exits the power-saving mode.
The WiMAX protocol specifies three different types of power-saving modes, which are collectively referred to as power-saving classes (PSCs), and are individually referred to as PSC I, PSC II, and PSC III. Generally, a subscriber station operating according to one of the WiMAX PSCs alternates between “sleeping,” where functionality is reduced to conserve power, and “listening,” where reception is powered on to determine if the serving base station is attempting to send data to the subscriber station. Each interval for which the subscriber station sleeps is referred to as a “sleep interval,” while each interval for which the subscriber station listens referred to as a “listening interval.”
According to 802.16e, when traffic arrives for a subscriber station that is in sleep mode, the subscriber station will receive a mobile-traffic-indication (MOB-TRF-IND) message from its serving base station, which indicates that traffic intended for the subscriber station has arrived at the base station. The MOB-TRF-IND message is typically sent such that the subscriber station receives the message during the listening interval immediately following the sleep interval where data intended for the subscriber station arrived. When operating according to PSC I, a subscriber station increases the size of the sleep interval after each successive listening interval during which no incoming traffic arrives for the subscriber station. PSC II is similar to PSC I, except that the size of the sleep interval remains constant, and does not increase.